The proposed research is an investigation of the dynamics of molecular processes which occur on the surface membranes of animal cells. The chief purpose is to understand how these processes contribute to the molecular mechanisms of control of growth, differentiation, and function in normal and cancer cells. Measurements of macroscopic lateral transport (diffusion and driven flow) of fluorescent labeled proteins and lipid analogues will be emphasized. These measurements are to be performed mainly by a new method, Fluorescence Photobleach Recovery (FPR) developed independently by ourselves and several other groups. In FPR a brief intense pulse of light bleaches the fluorophores in a small region of the cell membrane. Diffusion coefficients and flow rates are deduced from the rate of recovery of fluorescence (measured at low excitation intensity) due to transport of unbleached fluorophores from adjacent areas into the bleached region. FPR is ideally suited to the aims of this project by its capability to measure transport rates in single cells (and even different regions of the same cell) containing relatively few (less than 10 to the 6th power) of the observed fluorescent molecules with minimal perturbation of the system. The major aspects of the project are: 1. Characterization of the mechanisms and constraints of plasma membrane proteins and lipids. 2. Examination of the role of lateral transport of defined membrane components in specific physiological processes. 3. Assessment of changes in membrane dynamic properties resulting from malignant transformation. 4. Studies on model systems. 5. Further development of methods and instrumentation.